This invention relates to a tilt lock mechanism for marine propulsion device and more particularly to an improved hydraulic tilt locking mechanism.
In connection with outboard drives such as either an outboard motor or the outboard drive portion of an inboard/outboard drive, it is the normal practice to provide angular adjustment of the outboard drive about a horizontally disposed tilt axis for achieving trim adjustment. In addition, it is also the normal practice to permit the outboard drive to be tilted up completely out of the water under some conditions. In addition, it is desirable to provide an arrangement wherein the outboard drive is permitted to pop up when an underwater obstacle is struck so as to prevent damage. The mechanism should, once the underwater obstacle is cleared, permit the outboard drive to return to its previously set trim position. Furthermore, when reverse thrust are encountered, it is desirable if the device is operative to hold the outboard drive against popping up under such reverse drive thrusts. Although many of these advantages can be enjoyed in conjunction with the use of hydraulic shock absorbing devices interposed between the outboard drive and the transom of the associated watercraft, the hydraulic shock absorbing mechanisms should not interfere with the operator's ability to tilt the outboard drive up to its out of the water condition and also to permit it to return to its normal condition.
In one of the more commonly used type of arrangements, a hydraulic cylinder and piston assembly is interposed between the outboard drive and the transom and embodies a shock absorbing valving arrangement so as to hold the outboard drive against reverse thrusts and also to permit it to pop up when the underwater obstacle is encountered. With such arrangements, the piston rod extends through one chamber of the hydraulic cylinder piston assembly and an arrangement must be employed to compensate for the changes in volume of the piston rod, depending upon the axial position of the associated piston. It is normally the practice to employ an inert gas acting over the hydraulic fluid so as to provide this compensation. Such arrangements, however, have a tendency to permit the inert gas to enter into the shock absorbing arrangement per se and thus significantly diminish the ability of the unit to resist reverse thrusts and absorb impacts.
In the copending application entitled "Tilt Lock Mechanism For Propulsion Device", Ser. No. 565,271, filed Dec. 27, 1983 in my name and the name of Takashi Iwashita and assigned to the assignee of this application, there is disclosed a tilt locking mechanism embodying an accumulator having an inert gas arrangement and disposed in such a manner so as to reduce the likelihood of the inert gas entering the hydraulic cylinder and piston assembly of the main unit. Although the arrangement shown in that device is particularly useful, it has been found that under some conditions, it may also permit the entry of the inert gas into the operating cylinder and piston assembly where it may become trapped.
It is, therefore, a principal object of this invention to provide an improved tilt locking mechanism for an outboard drive that employs a gas over oil arrangement and in which the gas cannot enter into the shock absorbing system.
It is a further object of this invention to provide a hydraulic shock absorbing assembly for an outboard drive using a gas accumulator to compensate for changes in volume of one of the shock absorbing chambers due to the use of a piston rod and in which the gas is effectively isolated from the shock absorbing arrangement.